1. Field of the Invention
The present invention relates to a magnetic tape cartridge of a single reel type wherein only one tape reel having a length of magnetic recording or reproducing tape wound therearound is employed.
2. Description of the Prior Art
The single-reel magnetic tape cartridge of the type referred to above is known in the art from, for example, the Japanese Laid-open Patent Publication No. 2000-339911. The single-reel tape cartridge disclosed therein makes use of a reel locking mechanism for avoiding an arbitrary rattling motion of the reel within the cartridge and also for avoiding any possible loosening of the magnetic tape wound around the reel.
The reel locking mechanism of the type referred to above is shown in FIG. 7 and includes a reel retainer 42 disposed within the hollow of a reel hub 41 of the single reel 40 and normally urged downwardly, as viewed therein, by the action of a coiled spring 43 to prevent the reel 40 from undergoing an arbitrary motion within the cartridge. This reel retainer 42 is guided by a crisscross-sectioned guide 44, provided on an upper panel of the casing, for movement up and down and, so long as the reel retainer 42 is normally urged downwardly by the coiled spring 43, an inverted crown gear 45 provided on the undersurface of the reel retainer 42 is meshed with a crown gear 46 provided on a bottom wall of the reel hub 41 (or a center portion of the lower reel flange encompassed by the hollow of the reel hub 41) to thereby prevent the reel 41 from undergoing an arbitrary motion about the reel hub and also from undergoing an arbitrary up and down movement in a direction parallel to the longitudinal axis of the reel hub 41.
The reel locking mechanism shown in FIG. 7 also includes a lock release member 47 made of a steel material by the use of any known press work to represent a generally trifurcated shape and is disposed between the reel retainer 42 and the bottom wall of the reel hub 41. This lock release member 47 is so designed and so operable that when this lock release member 47 is urged upwardly against the biasing force of the coiled spring 43, the inverted crown gear 45 is disengaged from the mating crown gear 46 to allow the reel 40 to be freely rotatable. Although at this time the lock release member 47 rotates together with the reel 40 when the tape cartridge is in use, the use is made of a bearing ball 48 which is freely rotatably received in the undersurface of the reel retainer 42 to minimize the frictional resistance during the rotation of the reel 40, which ball 48 urges the lock release member 47 downwardly.
However, when the tape cartridge is not in use, i.e., is not loaded in the tape recording/reproducing apparatus, in order to retain the reel 40 in position without undergoing a lateral displacement in a direction generally perpendicular to the longitudinal axis of the reel hub 41, a ring-shaped engagement projection 49 is provided on the undersurface of that bottom wall of the reel hub 40 such that the engagement projection 49 can be held in abutment with an inclined inner peripheral wall 51 defining a drive access hole 50 that is defined in a center portion of the bottom panel of the casing. In other words, the inner peripheral wall 51 of the drive access hole 50 is so inclined as to diverge upwardly as viewed in FIG. 7 and, on the other hand, the engagement projection 49 has an outer wall surface so inclined as to converge downwardly, such that the engagement projection 49 can fit into the drive access hole 50 to thereby prevent the lateral displacement of the reel 40.
When and so long as the reel 40 is held in position with the engagement projection 49 fitted into the drive access hole 50, it is possible to avoid a displacement of the reel 40 relative to a drive shaft that is incorporated in the tape recording/reproducing apparatus for driving the reel within the cartridge. However, a problem has been recognized in that since the outer peripheral surface of the engagement projection 49 and the inner peripheral surface 51 each represent a simple tapering interface, the reel 40 may often displace laterally with the engagement projection 49 riding over the inclined peripheral surface 51 onto an inner surface of the bottom panel of the casing as clearly shown in FIG. 7, when an external force or impact acts on the cartridge in a direction generally transverse of the reel hub 40, resulting in the reel being held in a tilted fashion within the casing. When the tape cartridge with the reel 40 so held in the tilted fashion is loaded into the tape recording/reproducing apparatus, the drive shaft will fail to property engage the drive teeth 52 provided in the undersurface of the bottom wall of the reel hub 41 and, in the worst case it may occur, a tape drive mechanism within the tape recording/reproducing apparatus will be physically damaged.